Blue Iris

Are any of your cams cloned? Reason I ask is that a clone won’t pull a separate stream but if you then make enough changes to the clone the BI will no longer see the cam as clone and therefore pull a separate stream for both the main cam and the clone.

Many thanks for the input on this - it's certainly given me clues about what to check for.

I've checked and none of the cameras are cloned.
The 10G NIC is a TP-Link TX401 and I've got hardware offloading enabled on everything.

In fact, I've now got two active NICs in there. The 10G is dedicated to NAS duties between the server and my workstation, whereas the 2.5G is for everything else (including Blue Iris). Those NICs are on different subnets an have all offload enabled (including checksum).

This solves the problem to some extent but not entirely. With Blue Iris not running I hit a consistent 1.1GB/s over the 10G link. With the Blue Iris service only running I see about ~900MB/s. With the Blue Iris management console open I see~600MB/s. CPU gets very high (>90%) on the last one that only reaches 600MB/s so it could be CPU constrained.

Interestingly DW spectrum can maintain over 1GB/s with the headless server running and with another PC on the network viewing all the camera feeds through the DW client. However, it drops tp 500MB/s if I open the client on the server.

I still don't understand what's going on here. The processor is a bit old - an i3-7100, so might be worth swapping that out to see if that fixes it. However, with Windows 10 running all the same programs on the same hardware (except I was using a 1Gb NIC), I didn't see any drop-off in file transfers due to Blue Iris running.